This invention relates to an optical film containing an anti-glare layer that is to be provided at the front of a liquid-crystal display, a plasma display or a CRT display in order to control the direction of external illumination or improve the visibility of texts or graphics being presented on the displays. The present invention also relates to an image display apparatus using the optical film.
The anti-glare layer as commonly used with image display apparatus such as a liquid-crystal display, a plasma display and a CRT display is primarily intended to prevent unwanted image formation or contrast drop due to reflection of extraneous light on the display""s surface. To this end, asperities are formed on the surface of the anti-glare layer so that it has lower reflectance due to principles such as surface scattering and optical interference; the so treated anti-glare layer is provided on the outermost surface of the display.
The front face of the liquid-crystal display or the CRT display may itself be rendered anti-glare property. To this end, asperities are formed on the surface of a layer by various techniques including coating with a resin containing transparent particles, sandblasting and embossing. The resulting layer scatters regular reflected light so that its amount is sufficiently reduced to achieve the intended anti-glare property.
However, whichever method is used, there still remain surfaces that are oriented parallel to the regular reflecting plane shown in FIG. 1, in which reference numeral 11 designates the external light source, 12 is the display, 13 is the eye point, and 14 is the screen which serves as the regular reflecting plane. Obviously, one cannot eliminate the regular reflection which has been deleterious to the visibility of texts and graphics being presented on the display.
The present inventors conducted intensive studies in order to solve the aforementioned problem of the prior art and improve the visibility of texts and graphics being presented on the display. As a result, they successfully developed an anti-glare layer capable of controlling the direction of light which is externally illuminating the display.
An object, therefore, of the present invention is to provide an optical film containing the anti-glare layer.
Another object of the present invention is to provide an image display apparatus using the optical film.
The first object of the invention can be attained by optical films containing anti-glare layers that are to be placed at the front of a display and which have the following characteristics.
According to the first object of the present invention, there is provided a first aspect of the present invention is a An optical film containing an anti-glare layer having irregularities on a surface thereof in the form of high or low spots, wherein the irregularities are arranged such that the value of NN determined by the sequence of the following steps of (i) to (iv) is 1,000 or less: (i) dividing the irregular surface of the optical film into 10,000 planes consisting of 100 planes on each side; (ii) calculating, for each divided plane, the standard deviation D of the distance between positions where adjacent high or low spots have peaks; (iii) determining the mean value M for the values of the standard deviation D for the 10,000 divided planes; and (iv) determining the number NN of divided planes for which the value of the standard deviation D is 50% of the mean value M or lower; and, wherein the frequency at which the angle of inclination to the regular reflecting plane as measured with an aperture of two square microns is 0.5 or less degrees is 2% or lower.
A second aspect of the present invention is an optical film containing an anti-glare layer having irregularities on a surface thereof in the form of high or low spots, wherein the irregularities are arranged such that the value of NN determined by the sequence of the following steps of (i) to (iv) is 1,000 or less: (i) dividing the irregular surface of the optical film into 10,000 planes consisting of 100 planes on each side; (ii) calculating, for each divided plane, the standard deviation D of the distance between positions where adjacent high or low spots have peaks; (iii) determining the mean value M for the values of the standard deviation D for the 10,000 divided planes; and (iv) determining the number NN of divided planes for which the value of the standard deviation D is 50% of the mean value M or lower; and, wherein the frequency at which the angle of inclination to the regular reflecting plane as measured on a one-square-micron basis is at least 0.25 degrees is 98% or higher.
A third aspect of the present invention is a optical film containing an anti-glare layer as set forth in the first aspect or the second aspect above, wherein a half-width relative to maximum peak of the distribution of the angle of inclination relative to the regular reflecting plane as measured on a one-square-micron basis is 1 degree or lower.
A fourth aspect of the present invention is a optical film containing an anti-glare layer as set forth in any one of the first to third aspects above, wherein shapes of the high or low spots on the surface are each in a conical shape having a circular or elliptical plane base.
The second object of the present invention can be attained by the following. According to the second object of the present invention, there is provided a fifth aspect of the present invention is a image display apparatus using the optical film containing an anti-glare layer as set forth in any one of the first to fourth aspect of the present invention above.
In the present invention, the optical films are used in sizes ranging from 1 cm to 50 cm on one side or in diameters ranging from 1 cm to 50 cm.